Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $156.95   10.674%   $173.7028   $173.70   $173.70   $173.70  
  Purchase #2 $241.99   5.696%   $255.7738   $255.77   $255.75   $255.80  
  Purchase #3 $25.94   4.252%   $27.043   $27.04   $27.05   $27.00  
  Purchase #4 $72.64   4.815%   $76.1376   $76.14   $76.15   $76.10  
  Purchase #5 $128.87   4.339%   $134.4617   $134.46   $134.45   $134.50  
  Purchase #6 $176.38   6.683%   $188.1675   $188.17   $188.15   $188.20  
  Purchase #7 $101.60   5.696%   $107.3871   $107.39   $107.40   $107.40  
  7 purchase totals = $904.37       $962.6735   $962.67   $962.65   $962.70